This research project is directed towards a study of the steroid metabolic activity of estrogen-receptor positive and estrogen-receptor negative human breast cancer as well as a correlation between the steroid metabolic activity and the clinical response to endocrine ablation or hormone therapy in female patients with advanced breast cancer. Estrogen-receptor content using the sucrose gradient and dextran-coated charcoal methods will be determined on tumor tissues obtained from patients with primary breast cancer and untreated patients with advanced breast cancer. The metabolism of pregnenolone, dehydroepiandrosterone, 16 alpha-hydroxydehydroepiandrosterone, estradiol and estrone will be carried out using the same tissues for which the estrogen-receptor content were determined as mentioned above. The steroid metabolites will be isolated and purified using thin-layer chromatography and the identity of the compound will be determined by crystallization to constant specific activity, derivative formation to the acetate, oxidation product or reduction product. Follow up of patients undergoing treatment using endocrine ablation or hormone therapy and response to therapy will be determined according to criteria used by the Medical Oncology group at the University of Minnesota (Appendix C).